Organic electroluminescent display device and fabrication method thereof

ABSTRACT

An organic electroluminescent display device and fabrication method thereof is provided. The device includes a first substrate having at least one thin film transistor; an electroluminescent unit formed on the first substrate and electrically connect to the thin film transistor; a first protective layer formed on the electroluminescent unit; a second protective layer formed on the first protective layer; and a third protective layer formed on the second protective layer and in contact with the first protective layer. The device further comprises a second substrate sealed to the first substrate to form the electroluminescent unit between the first substrate and second substrate. In the device, the first protective layer comprising inorganic material, the second protective layer comprising organic material and the third protective layer comprising inorganic material are formed on the electroluminescent unit to reduce oxidation of electrodes by preventing infiltration of moisture.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to organic electroluminescent display devices, andmore particularly to an organic electroluminescent display device havingimproved waterproof capabilities and a fabrication method thereof.

2. Description of the Related Art

Organic electroluminescent display devices possess advantages ofimproved color, viewing angle, brightness and reduced size when comparedwith conventional displays, such as cathode ray tube (CRT) displays orliquid crystal displays (LCD). Thus, demand for organicelectroluminescent display devices is increasing. Organicelectroluminescent display devices are however easily affected bymoisture, such as oxidation of electrodes and components, shorteninglife. Thus, encapsulated structures and fabrication of organicelectroluminescent display devices is important.

FIG. 1 shows a conventional organic electroluminescent display device. Afirst electrode 12 is formed on a first substrate 10. Thereafter, anorganic electroluminescent layer 14 and a second electrode 16 aresequentially formed on the first electrode 12 followed by covering aprotective layer 18 on the second electrode 16. Finally, a secondsubstrate 20 is disposed on the first substrate 10. The waterproofability of the device suffers due to the use of only a single protectivelayer. Furthermore, a total thickness of the device is increased whenthe protective layer is increased.

Thus, an organic electroluminescent display device having improvedwaterproof ability without increasing thickness and method forfabricating is needed.

BRIEF SUMMARY OF INVENTION

The invention provides organic electroluminescent display devices. Anexemplary embodiment of the device comprises a first substrate having atleast one thin film transistor (TFT); an electroluminescent unit formedon the first substrate and electrically connected to the thin filmtransistor; a first protective layer formed on the electroluminescentunit; a second protective layer formed on the first protective layer;and a third protective layer formed on the second protective layer andin contact with the first protective layer. The device further comprisesa second substrate sealed to the first substrate forming theelectroluminescent unit between the first substrate and secondsubstrate.

The device further comprises a top area of the second protective layerin contact with the third protective layer greater than or equal to abottom area of the second protective layer in contact with the firstprotective layer.

The device further comprises a distance between top edges of the secondprotective layer in contact with the third protective layer greater thanor equal to a distance between bottom edges of the second protectivelayer in contact with the first protective layer.

The invention further provides a method for fabricating an organicelectroluminescent display device. The method comprises providing afirst substrate having at least one thin film transistor; forming anelectroluminescent unit on the first substrate and electricallyconnected to the thin film transistor; forming a first protective layeron the electroluminescent unit; forming a second protective layer on thefirst protective layer; and forming a third protective layer on thesecond protective layer and in contact with the first protective layer.The method further comprises the second protective layer is formed byink-jet printing (IJP) or screen printing.

The organic electroluminescent display device effectively preventsinfiltration of moisture into the electroluminescent unit for reducingoxidation of electrodes. Because the first protective layer comprisesinorganic material, the second protective layer comprises organicmaterial and the third protective layer comprises inorganic material areformed on the electroluminescent unit moisture infiltration isprevented. Additionally, stress between the first protective layercomprising inorganic material and the third protective layer comprisinginorganic material is relieved by the second protective layer comprisingorganic material formed therebetween. Further the second protectivelayer is only formed in a recess over the electroluminescent unit, thus,fabrication cost is reduced. The second protective layer formed in therecess over the electroluminescent unit provides improved organicelectroluminescent display device waterproof capability is withoutincreasing total thickness. Accordingly, life of the organicelectroluminescent display device is increased.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 depicts a cross sectional view of a conventional organicelectroluminescent display device;

FIG. 2A through FIG. 2H depict cross sectional views of forming anorganic electroluminescent display device according to first embodimentof the invention;

FIG. 3A through FIG. 3F depict cross sectional views of forming anorganic electroluminescent display device according to second embodimentof the invention; and

FIG. 4 depicts cross sectional view of an organic electroluminescentdisplay device according to third embodiment of the invention.

DETAILED DESCRIPTION OF INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

FIG. 2A through FIG. 2H, show cross-sectional views of forming anorganic electroluminescent display device according to a firstembodiment of the invention. In this embodiment, a color filter and thinfilm transistor serving as a switch may be disposed on the samesubstrate in the organic electroluminescent display device. That is, thecolor filter may be formed on the substrate on which the thin filmtransistor is formed.

As shown in FIG. 2A, a color filter 204 is formed on a first substrate200 having a plurality of thin film transistors (TFTs) 202 formedthereon. The first substrate 200 is transparent material, such as, glassor plastic. The flexible transparent material may also be used in firstsubstrate 200.

The thin film transistor 202, serving as a switch, includes a gateelectrode 2021, a source 2025 and drain 2023, in which the gateelectrode 2021 is formed on the first substrate 200 followed byformation of the source 2025 and drain 2023 thereon. The gate electrode,source and drain may be formed by well known conventional methods, thusfor brevity, description thereof is not provided in the following.

FIG. 2A, a dielectric layer 203 is formed on the first substrate 200 andcovers the TFTs 202 for protection and isolation. In one embodiment, thedielectric layer 203, for example, silicon oxide, silicon nitride orother suitable dielectric material may be formed by chemical vapordeposition (CVD), such as, low-temperature chemical vapor deposition(LTCVD), plasma enhanced chemical vapor deposition (PECVD) orlow-pressure chemical vapor deposition (LPCVD).

The color filter 204 is subsequently formed on the dielectric layer 203on the first substrate 200, as shown in FIG. 2A. In one embodiment, thecolor filter 204 is disposed on a portion of the first substrate 200under which no TFTs 202 are formed. Additionally, the TFTs 202 may serveas a shielding layer, for example, a black matrix (BM). Thus, theshielding layer may not necessarily be formed in the organicelectroluminescent display device thus, fabrication cost may be reduced.

In some embodiments, the color filter 204, comprising red pigment, greenpigment and blue pigment, is coated on the first substrate 200 byink-jet printing (IJP). The color filter 204 is then baked. The colorfilter 204 is preferably an organic color photoresist or any suitablematerial serving as a color filter.

FIG. 2B, an overcoat layer 206 is formed on the first substrate 200, andcovers the color filter 204 and TFTs 202 to planarize a surface of thefirst substrate 200. The overcoat layer 206 is preferably photosensitivematerial formed by spin-coating. The overcoat layer 206 is subsequentlypatterned, by photolithographic and etching processes to form a contacthole 207 exposing the drain 2023 of the TFTs 202.

After the contact hole 207 is formed, a first electrode 208 is formed onthe overcoat layer 206 and extended to the contact hole 207 forelectrically connecting to the drain 2023 of TFTs 202, as shown in FIG.2B. In one embodiment, the first electrode 208 is preferably atransparent conductive layer, such as, indium tin oxide (ITO) formed by,for example, sputtering. Photolithographic and etching processes thenpattern the conductive layer to form the first electrode 208. The firstelectrode 208 is correspondingly disposed on the color filter 204 formedon the first substrate 200. The first electrode 208 may act as an anodeof a subsequent electroluminescent unit and is referred to as an anodeelectrode.

In FIG. 2C, a pixel define layer (PDL) 210 having a plurality ofopenings 209 is formed on the first substrate 200 to form a pixel area212. The first electrode 208 is exposed by the openings 209. In oneembodiment, a pixel define layer 210 of photosensitive material forexample, is formed on the first substrate 200 and covers the firstelectrode 208 by, for example spin-coating. The pixel define layer 210is patterned to form openings 209 exposing the first electrode 208.

Note that the pixel area 212 is correspondingly formed on the firstelectrode 208 and color filter 204. Additionally, a distance between topedges of the pixel area 212 is greater than or equal to a distancebetween bottom edges of the pixel area 212 in contact with the firstelectrode 208.

In FIG. 2D, an organic electroluminescent layer 214 is formed on thefirst electrode 208 inside the pixel area 212 to provide a light sourcefor the organic electroluminescent display device. In one embodiment,the organic electroluminescent layer 214 may be, for example, a stack ofa blue emitting layer, red emitting layer and green emitting layer or ablue emitting layer doped with yellow emitting material (or red emittingmaterial) formed by, for example, vacuum evaporation to provide a whitelight for the organic electroluminescent display device. In anotherembodiment, a hole injection layer (not shown) and a hole transportlayer (not shown) are sequentially formed on the first electrode 208prior to formation of the organic electroluminescent layer 214. Afterthe organic electroluminescent layer 214 is formed, an electrontransport layer (not shown) and an electron injection layer (not shown)are formed on the organic electroluminescent layer 214.

In FIG. 2E, a second electrode 216 is conformally formed on the firstsubstrate 200 and covers the pixel define layer 210 and the organicelectroluminescent layer 214. The second electrode 216, organicelectroluminescent layer 214 and first electrode 208 inside the pixelarea 212 constitute an electroluminescent unit 217, in which the secondelectrode 216 may act as a cathode electrode of the electroluminescentunit 217. In one embodiment, the second electrode 216 is, for examplealuminum, aluminum-lithium alloys or magnesium-silver alloys, formed bysputtering, electron beam evaporation or thermal evaporation.

Note that the electroluminescent unit 217 comprising the first electrode208, organic electroluminescent layer 214 and second electrode 216 isdisposed on the color filter 204. While a current is provided to theelectroluminescent unit 217, an electron provided by the secondelectrode 216 combines with a hole provided by the first electrode 208in the organic electroluminescent layer 214 to emitting a light throughthe first electrode 208, color filter 204 and first substrate 200 andoutside the organic electroluminescent display device.

As shown is FIG. 2F, a first protective layer 218 is conformally formedon the second electrode 216. In one embodiment, the first protectivelayer 218 may be formed by, such as, vacuum evaporation, sputtering orplasmas enhanced chemical vapor deposition (PECVD) and have a thicknessof between about 0.1 μm and 0.5 μm.

Preferably, the first protective layer 218 may be an inorganic material,for example, metal oxide, metal nitride, metal carbide, metal oxynitrideor combinations thereof. The metal oxide is preferably silicon oxide(SiO_(x)), aluminum oxide (Al2O₃), titanium oxide (TiO₂), indium oxide(In₂O₃), tin oxide (SnO₂), indium tin oxide (ITO) or combinationsthereof. The metal nitride is preferably aluminum nitride (AlN), siliconnitride (SiNx) or combinations thereof. The metal carbide may be siliconcarbide (SiC) and the metal oxynitride may be silicon oxynitride (SiON).

FIG. 2F, a second protective layer 220 is then formed on the firstprotective layer 218 over the electroluminescent unit 217. The secondprotective layer 220 is disposed in a recess 209 over theelectroluminescent unit 217. In some embodiments, the second protectivelayer 220 is coated on the first protective layer 218 by ink-jetprinting (IJP). Note that a top surface of the second protective layer220 and a top surface of the first protective layer 218 aresubstantially planar because the second protective layer 220 is disposedin the recess 209.

A curing step, for example, thermal curing or light curing issubsequently performed. The curing step is selected base on the materialof the second protective layer 220. For example, if the secondprotective 220 is thermal-curable resin, a thermal process cures thesecond protective layer 220. In another example, if the secondprotective layer 220 is photosensitive (photo-curable) material,ultraviolet or visible light cures the second protective layer 220. Inone embodiment, the second protective layer 220 may have a viscosity ofbetween about 1 cp and 1000 cp. In another embodiment, the secondprotective layer 220 is formed in the recess 219 over the firstprotective layer 218 by screen printing.

Preferably, the second protective layer 220 may be a photo-curablematerial, for example, epoxy resin, or a thermal-curable material, suchas, an acrylic-containing polymer. Note that a distance between topedges of the second protective layer 220 is greater than or equal to adistance between bottom edges of the second protective layer 220 incontact with the first protective layer 218. An upper surface of thesecond protective layer 220 is substantially planar to an upper surfaceof the first protective layer 218 because the second protective layer220 is formed on the first protective layer 218 over theelectroluminescent unit 217.

In FIG. 2G, a third protective layer 222 is formed on the firstsubstrate 200, and contacts an upper surface of the first protectivelayer 218. In some embodiments, the third protective layer 222 may beformed on surfaces of the first protective layer 218 and the secondprotective layer 220 by vacuum evaporation, sputtering or plasmasenhanced chemical vapor deposition (PECVD). The third protective layer222 preferably has a thickness of between about 0.1 μm and 0.5 μm. Thethird protective layer 222 may be a material similar to the firstprotective layer 218, thus, further description is not provided.

Note that a top area of the second protective layer 220 in contact withthe third protective layer 222 is greater than or equal to a bottom areaof the second protective layer 220 in contact with the first protectivelayer 218. That is, a distance (symbol b, as shown in FIG. 2G) betweentop edges of the second protective layer 220 in contact with the secondprotective layer 222 is greater than or equal to a distance (symbol a,as shown in FIG. 2G) between bottom edges of the second protective layer220 in contact with the first protective layer 218, as shown in FIG. 2G.Additionally, the distance between bottom edges of the second protectivelayer 220 in contact with the first protective layer 218 is greater thanor equal to a distance (symbol c, as shown in FIG. 2G) between bottomedges of the organic electroluminescent layer 214 in contact with thefirst electrode 208. That is, a bottom width of the second protectivelayer 220 is greater than or equal to a bottom width of the organicelectroluminescent layer 214, as shown in FIG. 2G.

Note that the first protective layer 218, second protective layer 220and third protective layer 222 in the first embodiment preferablycomprises be transparent material as well as the second electrode 216.

In FIG. 2H, a second substrate 228 is subsequently disposedcorrespondingly on the first substrate 200 by a sealant 226 under avacuum or a nitrogen or argon containing atmosphere, and a buffer layer224 is formed therebetween, thus completing fabrication of an organicelectroluminescent display device of a first embodiment of theinvention. The second substrate 228 may be a material similar to thefirst substrate 220, however, a plastic film serving as an encapsulatingplate, for example, a plastic film with a waterproof layer may also beused. The sealant 226 is preferably a bonding agent containing epoxy.

When a current is provided to an electroluminescent unit, an electronprovided by the second electrode combines with a hole provided by thefirst electrode in the organic electroluminescent layer to emit a lightthrough the first electrode, color filter and the first substrate andexiting through the organic electroluminescent display device, as shownby the arrow in FIG. 2H.

The organic electroluminescent display device according to theembodiment of the invention effectively prevents infiltration ofmoisture into the electroluminescent unit because the first protectivelayer comprising inorganic material, the second protective layercomprising organic material and the third protective layer comprisinginorganic material are formed on the electroluminescent unit.Additionally, forming the second protective layer comprising organicmaterial between the first protective layer comprising inorganicmaterial and the third protective layer comprising inorganic materialrelieves stress between the first and third layers. The secondprotective layer is only formed in the recess over theelectroluminescent unit, thus, fabrication cost is reduced. Waterproofcapability of the organic electroluminescent display device is enhancedwithout increasing total thickness of the organic electroluminescentdisplay device because the second protective layer is formed in therecess over the electroluminescent unit. Thus, life of organicelectroluminescent display device is increased.

FIG. 3A through FIG. 3F show cross sectional views of forming an organicelectroluminescent display device according to second embodiment of theinvention. In the second embodiment, color filter and thin filmtransistor are disposed on different substrates.

FIG. 3A, a reflective layer 306 is formed on a first substrate 300having a plurality of thin film transistors (TFTs) 302, in which thereflective layer 306 is placed over a portion of the first substrate 300under which no TFTs 302 are formed. A dielectric layer 303 and overcoatlayer 304 are sequentially formed on the first substrate 300 and coverthe TFTs 302 before the reflective layer 306 is formed. Formation andmaterial of TFTs 302, dielectric layer 303 and overcoat layer 304 overthe first substrate 300 may be similar to the first embodiment. In someembodiments, a metal layer, for example, aluminum is formed on theovercoat layer 304 over the first substrate 300 by, for example,sputtering or evaporation. The metal layer is then patterned to form thereflective layer 306 on a portion of the first substrate 300 on which noTFTs 302 are formed.

In FIG. 3A, a first electrode 308 is formed on the reflective layer 306and electrically connected a drain 3021 of the TFTs 302 by passingthrough a contact hole 307. In some embodiments, the reflective layer306 and a portion of the overcoat layer 304 is masked by a patternedphotoresist (not shown) followed by removing a portion of the overcoatlayer 304 and dielectric layer 303 to form the contact hole 307 forexposing the drain 3021 of the TFTs 302. A transparent conductive layer,for example, indium tin oxide (ITO) is then formed on the overcoat layer304 and covers the reflective layer 306 after removing the patternedphotoresist. Thereafter, the transparent conductive layer is patternedto form the first electrode 308 on the reflective layer 306 andelectrically connect to the drain 3021 of the TFTs 302 by passingthrough the contact hole 307. The formation and material of the firstelectrode 208 is preferably similar to the first embodiment. The firstelectrode may function as an anode electrode for a subsequently formedelectroluminescent unit.

FIG. 3B, a pixel define layer 310 having a plurality of openings 309 isformed on the first substrate 300 to form a pixel area 312. The firstelectrode 308 over the reflective layer 306 is exposed by the openings309. Preferably, a distance between top edges of the pixel area 312 isgreater than or equal to a distance between bottom edges of the pixelarea 312 in contact with the first electrode 308. Formation and materialof the pixel define layer 310 may be the same as the first embodiment,thus, further description is not provided.

FIG. 3C, an organic electroluminescent layer 314 is formed in the pixelarea 312 followed by covering a second electrode 316 on the organicelectroluminescent layer 314 and the pixel define layer 310. The firstelectrode 316, the organic electroluminescent layer 314 and the secondelectrode 316 in the pixel area 312 constitute an electroluminescentunit 317, in which the first and second electrodes 308 and 316 serve asan anode and cathode, respectively. Formation and material of theorganic electroluminescent layer 314 and second electrode 316 may besimilar to the first embodiment.

As shown in FIG. 3D, a first protective layer 318 is formed on thesecond electrode 316 followed by formation of a second protective layer320 on the first protective layer 318 over the electroluminescent unit317. Preferably, the first protective layer 318 may be, for example,inorganic material similar to first embodiment formed on the secondelectrode 316 by vacuum evaporation, sputtering or plasma enhancedchemical vapor deposition. The first protective layer has a preferablythickness of between about 0.1 μm and 0.5 μm.

In some embodiments, the second protective layer 320, for example,organic material is coated on the first protective layer 318 over theelectroluminescent unit 317 by ink-jet printing (IJP). Thereafter, acuring step, for example, thermal curing or light curing is performed tocure the protective layer 320 in a recess 319 over theelectroluminescent unit 317. The curing step is selected based onmaterial of the second protective layer 320. For example, the secondprotective layer 320 is cured by thermal process, when the secondprotective layer 320 is thermal-curing resin. In another example, thesecond protective layer 320 is cured by ultraviolet or visible light,when the second protective layer 320 is photosensitive material. In oneembodiment, the second protective layer 320 may have a viscosity ofbetween about 1 cp and 1000 cp. In another embodiment, the secondprotective layer 320 may be formed inside the recess 319 of theprotective layer 310 over electroluminescent unit 317 by screenprinting. Note that an upper surface of the second protective layer 320and an upper surface of the first protective layer 318 are substantiallyplanar because the second protective layer 320 is disposed in the recess319. The second protective layer 320 may comprises a material similar tothe first embodiment, thus, further description is not provided.

In FIG. 3E, a third protective layer 322, for example inorganicmaterial, is formed on the first substrate 300 and contacts surfaces ofthe first protective layer 318 and second protective layer 320.Preferably, the third protective layer 322 has thickness of betweenabout 0.1 μm and 0.5 μm. Formation and material of the third protectivelayer 320 may be the same as that of the first embodiment.

Note that a top area of the second protective layer 320 in contact withthe third protective layer 322 is greater than or equal to a bottom areaof the second protective layer 320 in contact with the first protectivelayer 318. That is, a distance (symbol b as shown in FIG. 3E) betweentop edges of the second protective layer 320 in contact with the thirdprotective layer 322 is greater than or equal to one (symbol a as shownin FIG. 3E) between bottom edges of the second protective layer 320 incontact with the first protective layer 318, as shown in FIG. 3E.Additionally, the distance between bottom edges of the second protectivelayer 320 in contact with the first protective layer 318 is greater thanor equal to a distance (symbol c as shown in FIG. 3E) between bottomedges of the organic electroluminescent layer 314 in contact with thefirst electrode 308. That is, a bottom width (symbol a as shown in FIG.3E) of the second protective layer 320 is greater than or equal to abottom width (symbol c as shown in FIG. 3E) of the organicelectroluminescent layer 314.

FIG. 3F, a second substrate 328 having a color filter 330 thereon, isthen correspondingly disposed on the first substrate 300 by a sealant326 under a vacuum or a nitrogen or argon containing atmosphere and abuffer layer 324 is formed therebetween, completing fabrication of anorganic electroluminescent display device according to the secondembodiment of the invention. The second substrate 328 may be similar tothe first substrate 300 or may be a plastic film with waterproof film.The sealant 326 is preferably a bonding agent containing epoxy. Thecolor filter 330 is correspondingly disposed over the electroluminescentunit in the pixel area and separated by a shielding layer 332, forexample black matrix. Formation or material of the color filter 300 maybe similar to first embodiment or any suitable formation or materialknown to those skilled in the art.

When a current is provided to an electroluminescent unit, an electronprovided by the second electrode (also referred to as cathode) combineswith a hole provided by the first electrode (also referred to as anode)in the organic electroluminescent layer to emit a light through thefirst electrode, color filter and the first substrate and the organicelectroluminescent display device, as shown by an arrow in FIG. 3F. Aportion of the light through the first electrode may, however, bereflected by the reflective layer, to then exit the organicelectroluminescent display device by way of the described path.

The organic electroluminescent display device according to secondembodiment of the invention effectively prevents oxidation of electrodesby infiltration of moisture into the electroluminescent unit. Becausethe first protective layer comprising inorganic material, the secondprotective layer comprising organic material and the third protectivelayer comprising inorganic material are formed on the electroluminescentunit to prevent moisture infiltration. Additionally, a stress betweenthe first protective layer comprising inorganic material and the thirdprotective layer comprising inorganic material is reduced by forming thesecond protective layer comprising organic material therebetween.Furthermore, the second protective layer is only formed in the recessover the electroluminescent unit, thus, fabrication cost is reduced.Furthermore, waterproof ability of the organic electroluminescentdisplay device is enhanced without increasing thickness of the organicelectroluminescent display device because the second protective layer isformed in the recess over the electroluminescent unit, thus, life isincreased.

Note that the first protective layer, second protective layer and thirdprotective layer is preferably a transparent material and the secondelectrode may be transparent material as well.

FIG. 4 shows a cross sectional view of an organic electroluminescentdisplay device according to third embodiment of the invention. Comparewith second embodiment, difference is that a color filter may befunction as a second protective layer, thus, similar element andformation can refer to above.

In FIG. 4, a first protective layer 418 is formed on a second electrode416, after a first electrode 410, an organic electroluminescent layer414 and the second electrode 416 is formed on a first substrate 400.Formation and material of the first protective layer 418 may be similarto the second embodiment. A second protective layer 420 comprising anorganic color photoresist is formed on the electroluminescent unit 417to function as a color filter. Preferably, is the described ink-jetprinting or screen printing forms the second protective layer 420.

A third protective layer 422 is then formed on the second protectivelayer 420 and in contact with the first protective layer 418 after thesecond protective layer 420 is formed. Finally, a second substrate 428is sealed to the first substrate 400 by a sealant 426. A buffer layer424 is filled between the first substrate 400 and second substrate 428,to complete an organic electroluminescent display device according to athird embodiment of the invention, as shown in FIG. 4.

Note that color filter and shielding layer is not necessarily formed onthe second substrate, thus, steps of fabrication and cost of materialutilized are reduced. A stress between the first protective layercomprising an inorganic material and third protective layer comprisingan inorganic material is reduced because the second protective layercomprises an organic photoresist. Note that the second protective layerin first embodiment may be a material of organic color photoresistfunction as protective layer and color filter to reduce fabricationcost, although it is not described here.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. To the contrary, it is intended to cover variousmodifications and similar arrangements (as would be apparent to thoseskilled in the art). Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar arrangements.

1. A method for fabricating an organic electroluminescent displaydevice, comprising: providing a first substrate having at least one thinfilm transistor; forming an electroluminescent unit on the firstsubstrate and electrically connected to the thin film transistor;forming a first protective layer on the electroluminescent unit; forminga second protective layer on the first protective layer; and forming athird protective layer on the second protective layer and in contactwith the first protective layer.
 2. The method as claimed in claim 1,further comprising forming a pixel define layer having a pixel area onthe first substrate, wherein the pixel area has an organicelectroluminescent layer therein.
 3. The method as claimed in claim 2,further comprising forming a recess over the electroluminescent unit,for containing the second protective layer.
 4. The method as claimed inclaim 1, wherein the second protective layer is formed by ink-jetprinting or screen printing.
 5. The method as claimed in claim 4,further comprising performing a curing step after forming the secondprotective layer.
 6. The method as claimed in claim 5, wherein thesecond protective layer has a viscosity of between about 1 cp to 1000 cpbefore the curing step.
 7. The method as claimed in claim 2, furthercomprising: forming a color filter layer on the first substrate underthe pixel area; and sealing a second substrate over a surface of thefirst substrate having the electroluminescent unit formed thereon. 8.The method as claimed in claim 2, further comprising: forming areflective layer on a portion of the first substrate under the pixelarea; and sealing a second substrate having a color filter layer formedthereon over the first substrate, wherein the color filter layer iscorrespondingly disposed on the reflective layer.
 9. An organicelectroluminescent display device, comprising: a first substrate havingat least one thin film transistor; an electroluminescent unit formed onthe first substrate and electrically connected to the thin filmtransistor; a first protective layer formed on the electroluminescentunit; a second protective layer formed on the first protective layer;and a third protective layer formed on the second protective layer andin contact with the first protective layer.
 10. The device as claimed inclaim 9, further comprising: a recess formed over the electroluminescentunit, wherein the second protective layer is contained inside therecess.
 11. The device as claimed in claim 9, wherein the firstprotective layer and the third protective layer comprise silicon oxide,aluminum oxide, titanium dioxide, indium oxide, tin oxide, indium tinoxide, aluminum nitride, silicon nitride, silicon carbide or siliconoxynitride.
 12. The device as claimed in claim 9, wherein the secondprotective layer comprises an organic material.
 13. The device asclaimed in claim 9, wherein the second protective layer comprises epoxyresin or acrylic-containing polymer.
 14. The device as claimed in claim9, wherein the second protective layer comprises color photoresist. 15.The device as claimed in claim 9, wherein a top area of the secondprotective layer in contact with the third protective layer is greaterthan or equal to a bottom area of the second protective layer in contactwith the first protective layer.
 16. The device as claimed in claim 9,wherein a distance between top edges of the second protective layer incontact with the third protective layer is greater than or equal to adistance between bottom edges of the second protective layer in contactwith the first protective layer.
 17. The device as claimed in claim 9,further comprising: a pixel define layer having a pixel area, formed onthe first substrate; and an organic electroluminescent layer disposed inthe pixel area.
 18. The device as claimed in claim 17, wherein a bottomwidth of the second protective layer is greater than or equal to abottom width of the organic electroluminescent layer.
 19. The device asclaimed in claim 17, further comprising: a color filter layer formed ona portion of the first substrate under the pixel area; and a secondsubstrate sealed over a surface of the first substrate having theelectroluminescent unit formed thereon.
 20. The device as claimed inclaim 17, further comprising: a second substrate correspondingly sealedover a surface of the first substrate having the electroluminescent unitformed thereon; a color filter layer formed on the second substrate andcorresponding to the pixel area; and a reflective layer disposed on aportion of the first substrate under the pixel area.